(a) Field of the Invention
The present invention relates to a locking device, especially to a steering column shaft locking device for an automotive vehicle.
(b) Description of the Prior Art
Coincidental locks have been equipped in steering columns to prevent theft of automotive vehicles, and as disclosed for example in U.S. Pat. No. 4,487,042, they are coupled with an ignition switch for controlling driving of the vehicle. Usually, a steering column locking device comprises a frame, a key cylinder mounted within the frame for rotation around its longitudinal central axis by a key between "LOCK" and "ON" or "START" positions through "ACC" position, a cam rotatable with the key cylinder, a locking rod in cooperation with the cam and a spring for moving between a locking position in which it is engaged with a steering shaft and an unlocking position in which it is disengaged from the steering shaft, and an ignition switch disposed rearward of the cam in driving relation thereto.
After the key is inserted into the key cylinder, it may be rotated around the longitudinal central axis from "LOCK" position to "OFF", "ACC" "ON" and "START" positions. In "ON" position, the ignition switch supplies electric power to an engine and in "START" position, a starter motor is energized to start the engine. When the key is pulled out of the locking device in "LOCK" position, rotation of the key cylinder to "ON" position is inhibited, and thereby, the steering shaft is prevented from rotation and the ignition switch can not be operated for anti-theft purpose.
Some of prior art steering shaft locking devices include key detecting means for sensing insertion of the key into the key cylinder. Prior art key detecting means comprises a first pin slidably disposed within the key cylinder, a second pin for detecting sliding movement of the first pin and a microswitch attached to an inner or outer surface of the locking device so as to be operated by movement of the second pin. The microswitch is attached to the locking device together with a plurality of additional parts such as fixing members and a harness connected to the switch. This structure obviously results in increased number of parts to be assembled, complicated assembling process and larger size of the locking device. To relieve these problems, a new and practical structure of steering lock devices has been required for many years.